Tumors result from aberrant, unrestrained proliferation of a single cell, generating a clone of transformed cells (47). Cancer is characterized by tumor cells' autonomous growth and metastasis to distant sites (48).
Tumor cells may express unique antigens that can be recognized by the immune system. Tumor-associated antigens include, but are not limited to, mutated oncogenes, mutated normal cellular proteins, aberrantly expressed cellular proteins, abnormal cell-surface proteins, and oncogenic viral proteins (49). Ideally, the immune system views these tumor-associated antigens as non-self, eradicating the tumor cells while sparing the healthy cells. Thus, identification of immunogenic tumor-associated antigens promotes clinical prognostic or therapeutic applications for cancer.
Such malignancies may be indicated in pleural effusion, excess fluid in the space between the lung and chest wall (50). Lung carcinoma, breast carcinoma, and lymphoma cause about 75% of all malignant pleural effusions (50). Malignant pleural effusion may be enriched with lymphocytic infiltrates and tumor cells. Tumor-associated immune complexes (1-3) or autoantibodies such as anti-p53 (4), antinuclear (5), and anti-L-Myc (6) antibodies have been found in effusion fluids and are associated with poor prognosis. Several lung tumor-associated antigens have also been identified in malignant effusion, including, cytokeratin 19 fragments, neuron-specific enolase (ENO2), squamous cell carcinoma antigen (7), and soluble HLA-I (8) etc.